This image from NASA's Cassini spacecraft shows an ancient southern sea that used to sprawl out near the south pole of Saturn's moon Titan. // photo by NASA/JPL-Caltech/ASI/Proxemy Research
The 44th annual meeting of the Division for Planetary Sciences of the American Astronomical Society
continued Tuesday in Reno, Nevada. Science talks ranged from studies of the atmospheres of planets as close as Mars and Jupiter to those hundreds of light-years away circling other stars, and to the latest results from Dawn’s mission to the asteroid Vesta.
But two of the most interesting stories came during a noontime press conference. In the first, Ellen Stofan of Proxemy Research in Gaithersburg, Maryland, reported on her team’s study of the lakes and seas of liquid hydrocarbons on the surface of Saturn’s moon Titan. As the Cassini spacecraft’s radar instrument has built up a picture of the satellite’s surface, scientists have found stark differences in the north and south polar regions. In the north, three large seas and hundreds of smaller lakes dot the surface; the south features only two partially filled basins.
The researchers considered the possibility that Titan might experience a climate cycle that transfers hydrocarbons from one pole to the other, and the north just happens to have the lion’s share now. But less than 50,000 years ago, the cycle would have been reversed and the south should have been inundated.
To test the hypothesis, the team looked for remnants of any southern seas by searching for features that show an ancient shoreline surrounding a large area of smooth plains. The scientists found two such regions that cover areas larger than roughly 40,000 square miles (100,000 square kilometers) and remnants of several other possible seas or large lakes. Interestingly, one of the possible seas now contains Ontario Lacus, the largest body of liquid hydrocarbons near the south pole. The team suspects that these features are largely dried-up seas from a time when this part of Titan was much wetter.
In the other presentation, Alan Stern of the Southwest Research Institute in Boulder, Colorado, presented an update on plans for the New Horizons spacecraft when it reaches Pluto in 2015. Stern, the mission’s principal investigator, mentioned that the countdown to Pluto will drop below 1,000 days later this week, a significant milestone in the craft’s 3,500-day journey.
He says the mission team is looking at possible new trajectories through the Pluto system. The reason: the discovery of three small moons orbiting the dwarf planet. If a small Kuiper Belt object collides with either Pluto or its big moon, Charon, any impact ejecta would fall back to the body. But a collision with one of the three small moons would unleash shards that could form a ring or cloud of debris permeating the whole system. And with New Horizons traveling at more than 30,000 mph (50,000 km/h), even a BB-sized shard could severely damage the spacecraft.
Mission planners are developing nine different alternatives — a plan they’ve dubbed the Safe Haven Bail Out Trajectory, or SHBOT. Some of the tracks pass Pluto significantly farther away than the original plan while others are just a little farther out. Scientists using large ground-based telescopes and the Hubble Space Telescope are searching for any debris, and New Horizons will get even better views as it approaches.
If something potentially dangerous shows up in the weeks or months before closest approach, the team likely will opt for one of the other trajectories. New Horizons will be able to change course up to 10 days before it reaches Pluto. A successful flyby not only will return the first close-up views of this distant world, but it also will keep the probe on track to visit a more distant Kuiper Belt object years later.
On the road: Planetary sciences in Reno, day 1